Vacuum metallizing a dielectric substrate with indium and products thereof

ABSTRACT

A surprisingly corrosion and abuse resistant plastic object vacuum-metallized with a corrosion prone metal, namely indium, on a dielectric substrate consists of minute specular electrically-discrete &#34;islands&#34; of the indium topcoated with a clear resinous layer which encapsulates and insulates the islands, one from another. The indium islands are less than one thousand angstroms thick and have an average diameter of less than three thousand angstroms. This island structure is secured by stopping the growth of the metal as it is deposited between the nucleation stage and the stage of channelization or formation of an electrically conductive film. The island structure permits the dielectric resinous topcoat to penetrate in, about and under the metal islands encapsulating and securely bonding them to the substrate. 
     The vacuum deposited indium gives a bright sheeny appearance which, when properly topcoated, very closely duplicates the appearance of electrodeposited chrome. A preferred application of this invention is the manufacture of exterior automobile trim components the base structure of which is a flexible elastomer such as a thermoplastic urethane.

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.133-857, "Vacuum Metallized Articles" filled Mar. 25, 1980 by thepresent inventor, now abandoned the description of which is incorporatedby reference.

PRIOR ART

Vacuum metallizing of plastic and similar dielectric substrates havebeen practiced for some time, see U.S. Patents:

    ______________________________________                                        2,992,125           Fustier                                                   2,993,806           Fisher                                                    3,118,781           Downing                                                   3,914,472           Nakanishi                                                 4,101,698           Dunning                                                   4,131,530           Blum                                                      4,211,822           Kaufman                                                   4,215,170           Oliva                                                     ______________________________________                                    

The automobile industry has had a desideratum for metallized trimcomponents that could be substituted for conventional chrome-platedmetal parts. See "Restoring the Luster to Metallized Markets", ModernPlastics, December, 1974, page 42, et seq. However, weather, abuse andcorrosion resistance of such metallized plastic parts has been marginaland their color match with electroplated chrome has been poor.

Work has been done in other fields with the vacuum depositing of indium,e.g. see Japanese Pat. No. 15812/78 by Nobuyoshi Fujihashi and HirooMiyamoto. Work has also been reported on the effect of vacuummetallizing conditions on the deposited metal grain structure. See"Influence of Substrate Temperature and Deposition Rate on Structure ofThick Sputtered Cu Coatings" by John A. Thornton, J. Vac. Sci. Technol.,Vol. 12, No. 4, July/Aug. 1975, page 830, et seq.

Recently some commercial products have been made. See "Sputtering inProduction at Chevrolet", Industrial Finishing, October 1979, describingthe Camaro Berlinetta grilles coated with a chrome alloy; "Alternativesto conventional Chrome Plated Plastics" by D. M. Lindsey of the GeneralMotors Chevrolet Engineering Center; and a "Critique on CurrentPreparation Techniques" by Hugh R. Smith, Jr. of Industrial VacuumEngineering, the latter two papers having been presented at the 1979Society of Vacuum Coaters Annual Conference; "Ion Plating Using a PureIon Source: An Answer Looking for Problems", by Hale et al, ElectronicsPackaging and Production, May 1975, pg. 39 et seq; and "ContinuousVacuum Metallizing", Modern Plastics, December, 1977, page 42 et seq.While these articles describe the supposed successful manufacture ofexterior automobile trim components that can reasonably be expected togive the performance required in service, they all fail to give theslightest hint that the vacuum metallized products do not look or appearas they should--that they are in fact substantially darker appearingthan electro-deposited chrome and thus do not have the bright sheenychrome look and showroom sparkle that a purchaser of a new automobileexpects and demands.

No reference has been found that relates metal film island structure andspacing to the appearance and performance of a commercial product, tothe conductivity of the metal layer, to the corrosion resistance of themetal layer and/or to the adhesion of the top coat. Nor does the priorart relate nucleation and film growth to a desired island structure andspacing that achieve these ends.

With regard to the last statement, two excellent reference books are:

Thin Film Phenomena, Katuri L. Chopra, Robert E. Kreiger PublishingCompany, Huntington, N.Y. 1979. See especially pp. 163 et seq.

Handbook of Thin Film Technology, Leon I. Maissel and Reinhard Glang,McGraw-Hill Book Company, New York, N.Y. 1970. See especially pp 8-32 etseq.

These texts discuss and illustrate the stages of metal film growth byvacuum deposition from metal nucleation and nuclei growth, to liquidcoalescence, to electrically discrete islands, channelization withincipient film conductivity and finally full continuous film formation.Film formatin of vacuum deposited metals on plastic substrates forcommercial products, especially on elastomeric plastic substrates is notdiscussed. Nor is the interdependence of the natures of the metal filmand the top coating correlated with product performance.

None of the references show an awareness of the significant differencein performance to be obtained with a vacuum metallized flexible plasticproduct, top coated, where the metal particles are coalesced only to theisland rate instead of being allowed to coalesce to beyond thechannelization stage where film conductivity is established. A carefulreading of the patent literature will show that while a patentee mayspeak of the metal film being in particle form, these particles haveresulted from the breaking up of a conductive coalesced continuous filmby application of a solvent-containing top coating with the solventattacking and causing swelling of the plastic base and consequentcracking and crazing. This cracking and crazing effect in most instancesis quite striking, occurring within a few seconds of the application ofthe liquid top coat. The "islands" or particles formed by top coating ofan electrically conductive metal film, while they may be electricallydiscrete after the top coat has been heat treated, are usually planarand have generally linear and angular corners as compared to therounded, coalesced islands of the present inventions. In the presentinvention, the separate islands have coalesced from separate nucleationpoints, are globular or rounded and fused appearing and are part of thenucleation and growth process. The islands formed by cracking aresubstantially larger on the average. They might better be termed"platelets" and can be likened to the cracked surface of a dried mudpuddle, which cracks are usually visible to the naked eye and detractfrom the appearance.

In general, the coalesced islands forming the indium films of thepresent invention are smaller and there is a much greater spacingbetween them that can be filled with the resin of the top coating, ineffect encapsulating the islands and binding them to the substratesurface. The rounded islands are better protected by the resin and thefilm over all is far more corrosion resistant, suprisingly so. The metalfilm is much more securely adhered to the substrate--a very significantadvantage. The appearance of the globular island product is better--itis more specular, more reflective.

The construction of the indium island structure on an organic substratedand top coated with a resinuous film gives a new product not heretoforeknown. All other metals heretofore deposited by vacuum evaporation bythe present inventor become conductive, i.e. grow beyond the islandstage, at a point where their light transmission is too high to beuseful.

In U.S. Pat. No. 3,118,781, while the patentee refers to the "particlesof the vapor-deposited metal layer" (Col. 4) in the same breath he saysthe applied top coat "will penetrate into minute or microscopic cracksor spaces" between them (emphasis added). This patentee vacuum depositsgold, an inherently corrosion-resistant metal, which by the time it isof a thickness to give sufficient reflectivity of visible light(4,000°-7,000°A) to be of interest, forms an electrically continuous andconductive layer. Following application of his top coating, (Col. 5,line 32 et seq) the patentee secured in increase in light transmission,which is consistent with crazing or cracking of a continuous metal filmhaving occurred during application of the top coat. The patentee uses an"Ultra thin" top coat because of the cohesion of the thin coating is notas great as its adhesion to the metal. His tape tests show that theresin does not flow about and encapsulate his metal particles and bondwell to the substrate under the platelets particles. Such an ultra-thincoating offers no physical protection to the metal film. In the presentinvention a top coat at least 1/2 mil thick is applied to impart goodabrasion resistance besides effecting the requisite encapsulation.

U.S. Pat. No. 4,215,170 speaks of "an extremely thin coat of metallicparticles deposited on a finely finished transfer agent." (Col. 2 lines11-12) Those skilled in the art will appreciate that "particles" arenot, cannot, be deposited from the vapor phase. Subsequently (Col. 4,line 23) the patentee refers to the "interstices or spaces between themetallic particles" following application of the top coat. Consideringthe metals (aluminum) and substrates (polypropylene) employed and themetal film thickness (105° A), it is obvious that his particles resultedfrom crazing of a continuous metal film. An aluminum film deposited tothat thickness is electrically conductive until top coated. To securethe discrete coalesced islands of this invention from spaced nucleationpoints, it is necessary that the melting point of the metal be lowenough, and the temperature of the receiving surface be high enough toeffect the desired liquid coalescence of the metal. This could nothappen to U.S. Pat. No. 4,215,170.

U.S. Pat. No. 4,101,698 says that a metal layer " is applied to theelastomeric film as a separate, discontinuous or captured, (sic)generally planar, reflective segments, preferably being applied inindividual microscopic dots by vacuum-deposition." (Col. 2, line 29 etseq.). As discussed in the textbook references, the "planar" stage ofparticle shape is reached only after there has been sufficientcoalesence for film formation While this patentee may have thought thathis "segments" were a result of the vacuum deposition, this was not thecase--it was the result of the fracturing of a continuous film byapplication of the top coat.

The fundamental fault with U.S. Pat. No. 4,101,698 is that this patenteedoes not describe a means or apparatus for securing the "microscopicdots" he desired to have by vacuum deposition. At Col. 6 line 67 etseq., the patentee says the metal is vacuum deposited "in discontinuousquantities, or separate planar reflective segments such as dots". Did heuse a screen or a grid of some type interposed between the source andthe substrate? The size of the "dots" is not specified and in allprobability they are ten to one hundred-fold times larger than thecoalesced islands here of concern. In the present invention, the metalis not "applied" as "microscopic dots" by "vacuum-deposition" (which isimpossible) but are formed into "dots" or coalesced islands during themetallization.

Neither U.S. Pat. No. 4,101,698 nor any other reference makes mention ofthe highly improved corrosion resistance that can be secured via theplacing of the metal in the coalesced island form. In fact, U.S. Pat.No. 4,101,698 states in Col. 2 that he prefers to use corrosionresistant metals with the preferred metal being chromium. Chromiumcannot be formed into the coalesced islands of the present invention onthe substrate and under the conditions disclosed in U.S. Pat. No.4,101,698.

U.S. Pat. No. 4,211,822 deposits indium on a plastic substrate. Carefulreading of this patent establishes that the patentee carried thedeposition of the indium through the coalescence stage to the pointwhere channelization has occurred such that there is an interconnectingnetwork of conductive paths and the metal film overall appears to beconductive. The corrosion resistance of this metal film because it isconductive overall would be terrible even if a relatively goodinsulating topcoat were placed over the metal film. This patenteeobviously had no appreciation of the advantage of limiting the growth ofthe metal nuclei to the coalesced island stage such that there would beno interconnecting electrically conductive pathways between thecoalesced islands and the particles would be "free-floating" as desiredin U.S. Pat. No. 4,101,698 and in the present invention. It is believedthat the theory of the patentee in U.S. Pat. No. 4,211,822, Col 2, line17 et seq. is an erroneous theory as it is not the supposedmelting/ductility of the metal that is permitting its formability asdesired by the patentee. Instead the coalescence of the metal has beencarried to a reticulate structure which accepts flexing and stretchingof the plastic undercoat without loss of the conductive electricalpathways.

The prior art has (1) not appreciated the possibility of vacuumdepositing a metal on an organic surface (which surface is "impure" andcauses a high nucleation rate) and arresting the film growth before thechannelization/conductive stage of file formation is reached, using ametal and conditions to achieve a sufficient reflectivity to be ofcommercial interest, or (2) relating the resulting island structure to adesired product performance.

PRESENT INVENTION

The present invention is an article of manufacture comprising an organicdielectric base or substrate having a smooth surface such as a moldedplastic, a macroscopically continuous-appearing very thin layer thereonof a vacuum deposited corrosion-prone metal, specifically indium andalloys thereof consisting predominantly of indium and acting in much thesame manner as pure indium. Preferably the alloys each have a meltingpoint in the range of 125° to 250° C. The metel is in the form of minutespecular electrically discrete rounded metal islands. There is atopcoating over the metal film of an intimately adhered clear dielectricresinous film encapsulating and protecting the metal particles, andbinding them firmly to the substrate.

This product is particularly useful in the automotive applications as anautomobile exterior trim component to replace heavier and more expensiveconventional chrome-plated metal parts.

The present invention is based on the finding that with a thin vacuummetallized layer if the indium layer as it is being deposited orcoalesced into electrically discrete islands and maintained electricallynon-conductive, the metal layer is corrosion resistant if adequatelytopcoated even though the indium is a metal that is especially corrosionprone. The indium film is non-conductive as deposited because the metalnuclei initially deposited from the vapor phase are allowed to grow inmolten phase only to a discrete island stage with the particles beingelectrically isolated from one another. The coating is kept quite thinand there is insufficient metal deposited to bring about a bridging orcoalescence of the metal particles and formation of an electricallyconductive film. The indium layer should have a nominal thickness lessthan 1000° A, preferably less than 600° A. By "nominal thickness" ismeant the thickness determined by the weight of metal deposited per unitarea as if a continuous film. An interferometer gives about the samereading.

The metal film on the other hand must be thick enough to reflectsufficient light, i.e. it must be opaque enough, to make the coatedarticle appear as a metal article. Desirably the film will pass lessthan 25% of the light incident thereon at an angle greater than 60°.With some metals, such as aluminum and silver it is impossible at apractical temperature, to vacuum deposit sufficient metal to give thedesired opacity and reflectivity and not to deposit so much as securefilm electrical conductivity, i.e. bridging between the metal islands.The nature and temperature of the substrate surface and the operatingcondition can be important in this regard. Generally speaking, theminimum useful nominal film thickness of the indium will be at least150° A.

If the individual metal islands have a diameter that is a fraction ofthe wave length of light, say a diameter of less than 3500° A,preferably less than 3000° A on the average, the metal layer is quitebright and specular and not milky or whitish as occurs when the islandsize exceeds about 4000° A. The appearance of an indium layer depositedaccording to this invention and top coated approximates that ofelectroplated chrome.

While vacuum metallized commercial products have heretofore been madefrom metals that are inherently corrosion resistant such as chromium orstainless steel, such vacuum metallized films are electricallyconductive, and dark and unsatisfactory appearing. They do not look likeelectrodeposited chrome.

The indium film can be deposited by thermal evaporization, sputtering,ion plating, induction heating, electron beam evaporization and likemethods. See Thin Film Technology, by Berry et al. D. Van NostrandCompany, Inc. Princeton, N.J., 1968, Lib. of Cong. 68-25817. Better ormore uniform coverage appears to be secured especially with threedimensional objects having corners, edges, or recesses if some atoms ofan inert gas such as argon are present in the vacuum chamber in excessof those required for the evaporation. The vacuum deposition ispreferably carried out at a vacuum of 5×10⁻³ Torr or less.

When the spacing between the metal islands of the film is such as tohave the metal film electrically non-conductive, improved adhesion ofthe protective plastic topcoat results. This adhesion can be measuredfor example by the Ford adhesion test, specification No. ESB-M2P-105 B,or the Chevrolet tape adhesion test, Specification No. CTZ VM003 AA.This improved adhesion appears to be related to the separation betweenthe individual metal islands or width of the channels, i.e. to thedistinctiveness of the islands, rather than to their diameter or size.The top coating in cross section appears to encapsulate the islands,extending around and under them to secure good wetting of and adhesionto the substrate surface.

A novel and important point of this invention is this feature ofencapsulating the metal islands to "fix" the electrical non-conductivityof the metal film and thus to increase manifold the corrosion resistanceof the film. If the integrity of the topcoat is broken and moistureenters it only causes oxidation of the metal islands contiguous to thebreak and the blight of the corrosion cannot travel along the plane ofthe film under the topcoat as it can with the usual vacuum metallizedand coated objects made with corrosion prone conductive metal film.

The resinuous topcoat also improves resistance to mechanical abuse.Clear moisture resistant acrylic, urethane, and like coatings applied asa latex and more preferably as a solvent solution are suitable. Forcritical applications the topcoat will be baked to assure that a goodtough continuous film is produced. The plastic film appears to fill theinterstices and voids between and around the individual metal islandsand helps further isolate one from another.

Any suitable dielectric, i.e. electrically insulating, material can beused to receive the vacuum deposited metal such as dry wood, glass, or aplastic. For the intended automobile trim component application acastable or moldable plastic is used, preferably an elastomer that istough and abuse resistant with some flexibility such an injectionmolding grade thermoplastic polyurethane (TPU). Such organic surfacesare "impure" relative to the quite pure or clean surface used for thework reported in the texts, supra. Such impure surfaces vastly increasethe amount of nucleation.

By "flexible elastomer" is meant a natural or synthetic thermoplastic orthermoset plastic or polymer having an extensibility of greater thanapproximately 30% as compared to "rigid" plastics which have anextensibility of less than 10%. Of course for many applications wherethe article will not be subjected to mechanical abuse or impact, rigidplastics are perfectly suitable such as for instrument cluster trim orgrills. Examples of suitable rigid plastics are polyolefins such as apolypropylene, a polyacrylonitrile-butadiene-styrene and apolycarbonate.

The nature of the flexible substrate does not appreciably affect theperformance of the applied coatings. The substrate cannot be so stiff orrigid that it will not serve its intended function as a flexible trimcomponent nor can it be too flexible or elastomeric. The present coatingsystem can be applied over such flexible substrates such as reactioninjection molded urethane, thermoplastic olefins and urethanes, nylon,rubber and polycarbonates. A suitable primer may be necessary to smoothor gain adherence to the substrate. The present coating system can, ofcourse, be applied and used with substantially more rigid substrates,but other methods of bright trimming such as electroplating might bemore economical to use on firm or hard surfaces.

The vacuum deposited metal layer "mirrors" the surface on which it isdeposited, i.e. the surface smoothness or roughness shows up in thedeposited metal layer. For bright specular parts it is preferred to havethe surface on to which the metal layer is deposited to be smooth aspossible. Flame or thermally reflowed urethanes are particularly usefulin this regard. Often it is desirable to overcoat the base plastic witha clear or pigmented basecoat of some sort prior to the carrying out ofthe vacuum deposition step. Pigmented prime coats can be used to obtainan initial levelling of the base plastic surface following which a clearor pigmented base coat can be applied to give a mirror smooth surface.These layers can be heat treated or baked as required to develop theirmaximum properties. If a urethane or other light sensitive substrate isused, weatherability of the article may be improved by using a pigmentedbase coat that prevents light penetration to the plastic base. Light canpass through the metallized layer in amounts sufficient to have adegrading effect on the lower plastic layers.

Sputtering and thermal evaporation are preferred methods of laying downthe metal layer although the use of ion plating, induction heating orelectron beam evaporation methods are not precluded so long as they areoperated and controlled to give the discrete electrical non-conductiveisland structure.

Following the deposition of the metal layer the clear plastic topcoat,preferably one resistant to moisture penetration, is applied. Generallythe thickness of the topcoat will be at least 1/2 mil. (0.0005 inches)thick (dry basis) and usually will not exceed 0.005 inches thick. Forflexible exterior automobile trim, the topcoat is necessarilyelastomeric and if thermo-setting, it can be thoroughly baked, forexample at 250° F. or so, to develop its maximum properties. The topcoatis formulated to adhere both to the metal as well as to the baseplastic. Acrylics and urethanes are preferred.

It has been found that with the flat or planar particulate structureobtained by causing crazing or cracking of an already electricallyconductive vacuum deposited metal film, the topcoat does not penetratethe particles and reach and wet the substrate surface well, resulting innoticeably poorer adhesion as well as poorer resistance to corrosionbecause of the close spacing of the particles. With the cracked filmsformed from a conductive metal film only in the order of 2% or so of theunderlying surface is exposed through the cracks whereas because of theshape and size of the channels of the film structure of the invention onthe order of 40% of the underlying surface is exposed. This helps toexplain the better top coat adhesions obtained with this invention.While this difference in open areas seems large, one should appreciatethat the channels in the structure of this invention are of a differentshape and of a much smaller width, -200°-300° A, and the islands aremuch smaller relative to those of the planar islands and channels(3000°-5000° A wide) formed by the cracking of a once electricallyconductive film. The channels' size and size of the islands of thenonconductive films of this invention are such relative to the wavelength of light that the film is quite specular and appears to becontinuous. In contrast the gross size of the channels and islands of acracked structure distort the reflected light and often causeiridescence.

As the metal film of the present invention exists as discrete islands,flexing or bending of the metal film will not result in the furthermacro cracking of the metal layer such that there is no objectionablechange in its appearance when the plastic part is bent or stretched andthe stress is released. No other type of metal layer is known that willnot crack or craze under this degree of flexing, bending and stretching.

The invention will now be described by way of the following examples andwith reference to the accompanying drawings.

DRAWINGS

FIG. 1 is a graph comparing the percent diffuse reflectance (theordinate) of a metallized coating of this invention against comparativecoatings at various wave lengths of visible light spectrum expressed innanometers (the axis). Except for Example A, all the samples weretopcoated.

FIG. 2 is a micro photograph taken with a scanning electron microscope(SEM) at 44,000 magnification of a conductive indium layer about 1200° Athick prepared by thermal evaporation. The view angle is 45° and thegrains have an average grain diameter of about 4500° A. The coatingwhile having an acceptable diffuse reflectivity before topcoating wasquite milky, was definitely conductive and had poor corrosion resistanceeven when topcoated.

FIG. 3 is a similar micro photograph of a similarly prepared indiumcoating except that the average size of the islands is about 1800° A, asize considered acceptable, and about 250° A thick.

FIG. 4 is a view of the island structure of an indium film at 83000magnification taken by transmission electron microscopy (TEM). Theresolution by TEM is far better than the SEM for showing the islandspacing or channel width.

FIG. 5 is a microphotograph for comparative purposes of a top coatedaluminum layer deposited to such a thickness that it was initiallyelectrically conductive.

EXPLANATION OF DRAWINGS

These data were obtained using a Thermal evaporator made by ConsolidatedVacuum Corporation, Rochester, N.Y. Unless otherwise described, flatplacques were prepared for testing. The reflectances were obtained withan Integrated Sphere Spectrophotometer, KSC-18 with specular componentincluded, Model ACS-500S, made by Applied Color Systems, Inc., U.S.Highway 1, Princeton, N.J. Diffuse illumination by an 18" diametersphere by a standard broad band light source was used according to themanufacturer's instructions (47 pages). A barium sulfate surface has adiffuse reflectance of 100% on this scale.

In FIG. 1, line A is a plot of the reflectance of conventionalelectroplated chromium surface, used as a standard goal or target.

Line B is an example of this invention, being about a 220° A thickcoating of indium with a clear topcoat, prepared as set out in theExample. It can be seen that the diffuse reflectance of the indiumcoating compares favorable with that of electro-deposited chrome. Theindium without the topcoat has a higher reflectance than that of thechrome but the addition of the topcoat tones the reflectance down towhat is shown.

Line C gives the reflectance of a sputtered chromium surface topcoatedwith the same topcoat as in B. It can be seen that sputtered chromium,which has a higher reflectance than chromium vacuum deposited by othertechniques, is substantially darker than electrodeposited chromium.

Line D is the chrome alloy used for the Camaro Berlinetta TPU grill asdescribed in the Industrial Finishing article, supra, the measurementhaving been obtained from the part itself. It can be seen that theappearance of the part is dark and unsatisfactory, which is why perhapsit is used in an unobtrustive location and manner.

Line E shows the least satisfactory metallized coating and yet thiscoating was touted by the Pennwalt Corporation, as being highlyreflective--as having "solved" the problem of bright metal plasticsfinishing. See the "Continuous Vacuum Metallizing" article supra, page45. These dates were obtained from a topcoated chromium alloy metallizedsample, the metal of which was thermally evaporated by Pennwalt.

Well prepared topcoated sputtered stainless steel is slightly darkerthan Line C.

The minimum resistance at which the vacuum metallized layer becomesconductive and corrosion prone is difficult to establish. By thefollowing procedure it was determined that a thin film of indium whendeposited with sufficient thickness has a resistivity of less than 1 ohmwhich jumped to over 100 megaohms as the deposited metal film was madethinner down to about 80 millimicrons or 800 °A. Intermediateresistivity values between these two could not be established. The testwas carried out with a Megger brand insulation tester supplied by theBiddle Company of Plymouth Meeting, Pa. Test strips of the vacuumdeposited indium were prepared on a dielctric plastic base. The stripswere 1/2" wide×1-1/1". A 1/2" section at each end was used for coppercontact pads from the tester, leaving a 1/2" square center section asthe test area. 500 volts were applied to the contact pads to obtain theindicated readings. By suitable calculations, it can be shown that the100+ megaohm resistance value translated, when considering the thicknessof the metal film, to a resistivity of 2.5 ohm cm.

FIG. 3 shows the granular, island surface of an indium coating thermallyevaporated onto a substrate plastic plaque having a composition as inExample I. The coating thickness was about 250 °A and the average grainsize was 1800 °A. The diffuse reflectivity of the coating (withouttopcoat) was 74%. The coating was non-conductive by the above test andwas corrosion resistant when topcoated.

A similar sample was prepared having an average particle size of about3600 °A. It had a reflectivity of 80% (not topcoated) but was hazy inappearance with a bluish cast. It was marginally non-conductive. Thegrains apparently had started to grow together.

The coating of FIG. 2 was milky in appearance, had a reflectivity of 82%(not topcoated), and was conductive with a grain size of 4500 °A whichdefinitely exceeds acceptable limits.

In FIG. 4 vacuum deposited indium film was microtomed to give slicesthat were 20 to 50 microns thick. These slices were encapsulated in anepoxy and were then microtomed or shaved to a tiny tip which containedthe sample. The tip was then microtomed into approximately 1000 °A thickspecimens which were floated onto tiny copper grids. A diamond microtomewas used to do this. Photographs were taken of the indium layer at 83000magnifications and 283000 magnifications. FIG. 4 is a view of the islandstructure of the indium film at 83000 magnification.

Transmission electron microscopy can give images at very highmagnifications with a resolution of less than 10 °A. A very narrow beamof high voltage electrons (100 KV) is passed through the sample,magnified and projected onto a fluorescent screen.

As can be seen from FIG. 4 the indium islands were eliptical and widelyseparated, which features could not be satisfactorily observed in thescanning electron microscope of a similar indium layer over the samebase coat. The angle of the slice in FIG. 4 was about 60° to the planeof the metal and the sample was about 1200 to 1500 °A thick, i.e. thepicture is not a true 90° edge view of the indium layer. The islanddiameters between the TEM and SEM pictures are very similar, around 1800to 2000 °A. The small dots around the larger islands, resolved down to30 °A in diameter, were probably clusters of indium atoms about tocoalesce with the larger islands.

The thickness of the indium layer was estimated from the TEM picture tobe 450 °A which is in fair agreement with the 390 °A figure obtained bymeasuring the layer interferometrically.

FIG. 4 conveys how it is possible for the resinous topcoat to penetratein and about the metal islands of the vacuum deposited metal film thathas never been consolidated to the point of conductivity, encapsulatingthe islands and bonding them to the substrate surface. As previouslyexplained the topcoat can penetrate the channels and in and about theparticles, reaching the substrate surface to secure good wetting andconsequently good bonding to that surface. This figure helps to explainthe difference in results obtained with the vacuum metallized coatingsof this invention and those obtained by fracturing or crazing vacuumdeposited consolidated or electrically continuous metal films because ofbasecoat swelling and/or differences in thermal expansion/contractionbetween the topcoat, metal layer and base structure when heat treatingto cure the topcoat.

FIG. 5 is a microphotograph taken at 200X magnification with a Normarskydifferential interference contrast objective of a thermally evaporatedvacuum deposited layer of aluminum carried to the point where the metallayer was 240 °A thick, continuous and electrically conductive. The basecoat was the same as in the following Example 1. The sample was topcoated with a top coat of an aliphatic urethane carried in a hexanedioladipate solvent, the same top coat as described in the followingExample 1. The application of the top coat caused the cracking shownbecause of expansion of the base coat by absorption of the top coatsolvent. The top coat was baked at 250° F. Note that the particles havea shape and spacing entirely different from those of the rounded islandsof this invention. The island structure of this invention issubstantially free of such platelet particles which have angular cornersand linear edges that complement like corners and edges of adjacentplatelets.

Several like samples were made using aluminum, chromium, a stainlesssteel and a combination of silver evaporated on a layer of stainlesssteel. All samples were thermally evaporated and deposited to athickness where the metal films were electrically conductive andunbroken prior to top coating. They were applied to the urethane basecoat of Example 1 and to an acrylic/urethane base coat, the top coat wasthereafter applied and the samples baked at either 150°, 180° or 250°.All cracked in the manner shown in FIG. 5 yielding a definite, flatplatelet structure.

Interestingly, gold and silver, which are not corrosion-prone metals,did not crack over this base coat upon application of the top coat andbaking. They did wrinkle badly (iris). The explanation for thisdifference may be that the elongation of those metals, i.e., theirunannealed maleabilities or ductilties, is much greater than those forindium, aluminum, chromium or the stainless steel.

EXAMPLES Example 1

The sample part is a 1980 Cougar Chin Grille, Chevrolet Part No.XR7-234, injection molded with Goodrich 58130 thermoplastic urethane(TPU). A urethane enamel basecoat is applied over the grille. It is astandard production item supplied by PPG Industries, as ESP3967. Thiscoating is a melamine modified blocked aliphatic urethane. This coatingis light stable and is pigmented white to block light from reachingnon-light stable substrates. The basecoat is thinned and sprayedaccording to manufacturer's instructions onto the properly cleanedsurface at room temperature to a thickness of 1.0+ or -0.2 mils (drybasis). The applied coating requires an air flash of 20 minutes and isthen baked for approximately 60 minutes at 250° F. to reach fullproperties.

After the grille is cooled to room temperature it is vacuum metallizedwith indium thermally evaporated at lower power from boats according tothe following procedure:

A bell jar is pumped down to 5×10⁻⁵ Torr and then backfilled with argonto 7×10⁻⁴ Torr. The pumping system for the bell jar consists of amechanical roughing pump, a silicone oil diffusion pump, and a liquidnitrogen coldtrap to minimize water vapor and outgassing in the belljar. The function of the argon backfill is to obtain better coverage onthree dimensional parts. 0.13 grams of high purity indium is flashevaporated from 0.010 mil thick tungsten boat (43/4" length, 1/8"dimple×11/2" long) connected in series to a 5 volt AC variabletransformer. The grille is rotated on a carousel at 20 RPM with sourceto substrate distance varying during rotation from 81/2" to 141/2". Thisgives a metal thickness on the part of 425 °A. Any suitable method ofvacuum metalizing can be used.

The top coat is a solvent based aliphatic urethane prepared from 753parts Union Carbide Hylene W, 506 parts Union Carbide PCP-0300polycaprolactone polyol, 240 parts hexanediol adipate, and 23 parts DowCorning DC-193 silicone. The topcoat is spray applied at 17% solids to athickness of 1+or-0.2 mils (dry basis). The coating is air flashed for20 minutes and then baked for 60 minutes at 250° F. to reach fullproperties.

The completed composite gives the following performance against the FordESB-M2P105-B Elastomeric Exterior Paint Performance specification:

1. Color-very specular and an excellent color match to chrome plate.

2. Adhesion-Pass.

3. Flexibility-Pass.

4. Water Resistance-Pass.

5. Weathering Resistance-Pass.

6. Thermal Shock Resistance-Pass.

7. Resistance to Water and Soap Spotting-Slight spotting.

8. Resistance to Acid Spotting-Pass.

9. Gasoline Resistance-Pass.

10. Oil Resistance-Pass.

11. Resistance to Scuffing-Pass.

12. Heat Resistance-Pass.

13. Chip Resistance-Acceptable, same as pigmented flexible exteriorcoatings.

14. Cold Flexibility-Pass.

15. Resistance to Galvanic Action-Pass.

In addition this composite passes the Ford Thermal Cycle-Corrosion Testfrom its Exterior Electroplating Specification ESB-MIP47-A.

Example 2

The sample part is a 1979 Ford Pinto Bezal, Part No. D7EB-16018-AWA,reaction injection molded from thermosetting urethane. The part isprimed with PPG DEL-32906 gray urethane primer to give a smooth surfacefor basecoat application. Application is according to manufacturer'sinstructions and the primer is sprayed to a 1.0+or-0.2 mil thickness.The bake for this coating is 10 minutes at 250° F. The basecoat, metallayer, and topcoat are the same as in Example No. 1.

Example 3

The part, basecoat, and metal layer are the same as in Example No. 1.The topcoat is Celanese 84-7609 urethane topcoat sprayed to a dry filmthickness of 1.0+or-0.2 mils. The coating is air flashed for 20 minutesand then baked one hour at 250° F. to reach full properties.

Example 4

The following table compares the light transmissions and thickness atwhich various metals deposited on various substrates by vacuumevaporation become electrically conductive and not useful in the presentinvention. It is to be noted that all of the metal films except that ofindium became conductive at light transmission far too high to be usefulfor the decorative usage purposes of this invention, i.e. for automobilebright trim. Also note that the indium film remained nonconductive andrelatively opaque over a range of organic substrate types.

    __________________________________________________________________________    TRANSMISSIONS AT WHICH METAL LAYERS DEPOSITED                                 BY VACUUM EVAPORATION BECOMES CONDUCTIVE ON                                   DIFFERENT SUBSTRATES                                                          (Thickness in °A; Light Transmission in %)                             Urethane & DuPont Mylar                                                                            Polyethylene                                                                           Glass                                           Base Coat of                                                                             Type D500 (Not Metallizing                                                                       Microscope                                                                             Polypropylene                          Example I  (Metallizing Grade)                                                                     Grade)   Slide    (Exxon PP-12B)                         __________________________________________________________________________    In 800° A                                                                       7%                                                                              1000° A                                                                       1% 1600° A                                                                       2%                                                                              1500° A                                                                       2%                                                                              1500° A                                                                       1%                              Ag 60° A                                                                       63%                                                                              45° A                                                                        65% 70° A                                                                        55%                                                                              70° A                                                                        63%                                                                              95° A                                                                        61%                              Al 80° A                                                                       75%                                                                              90° A                                                                        70% 90° A                                                                        70%                                                                              80° A                                                                        75%                                                                              95° A                                                                        55%                              Au 75° A                                                                       70%                                                                              40° A                                                                        73% 60° A                                                                        60%                                                                              40° A                                                                        75%                                                                              65° A                                                                        63%                              Cr 75° A                                                                       60%                                                                              50° A                                                                        70% --    -- 50° A                                                                        70%                                                                              140° A                                                                       65%                              __________________________________________________________________________

The full names and addresses of companies mentioned supra are:

    ______________________________________                                        Chevrolet      Chevrolet Motor Division                                                      Flint, Michigan                                                Goodrich       B. F. Goodrich Company                                                        3135 Euclid Avenue                                                            Cleveland, Ohio 44115                                          PPG Industries PPG Industries                                                                3800 W. 143rd Street                                                          Cleveland, Ohio                                                Union Carbide  Union Carbide                                                                 Chemicals and Plastics                                                        South Charleston,                                                             W. Virginia 25303                                              Celanese       Celanese Chemical Company,                                                    Inc.                                                                          1481 South 11th Street                                                        Louisville, Kentucky 40208                                     Ford           Ford Motor Company                                                            Dearborn, Michigan                                             Exxon          Esso Chemical Co.,                                                            60 W. 49th Street                                                             New York, New York 10020                                       ______________________________________                                    

What is claimed is:
 1. A process of manufacturing a corrosion-resistantvacuum metallized article comprising:a. preparing a dielectric substratesurface and maintaining the same in a vacuum; b. vacuum depositing onsaid substrate surface a metal selected from the group consisting ofindium and alloys thereof consisting predominantly of indium; c. whilecontinuing said vacuum depositing effecting formation of discreteislands of said metal said islands appearing macroscopically as acontinuous film and transmitting therethrough less than 25% of thevisible light incident thereon at an angle greater than 60° to thesurface thereof but being electrically nonconductive over said surface;d. applying a clear resinous protective dielectric top coat as a liquidover and between said discrete islands and wetting said substratesurface with said liquid; and e. drying said top coat so applied to aprotective film encapsulating said discrete islands and intimatelyadhering said protective film to said substrate surface.
 2. The processof claim 1 wherein said islands under microscopic examination appearrounded in both plan and elevation view and to having been coalesced inliquid phase from small nuclei, said islands having an average diameterof less than 3500 °A, wherein said continuous film has a nominalthickness in the range of 150 to 1000 °A and wherein said top coat is atleast 1/2 mil. thick (dry basis).
 3. The process of claim 1 wherein thesubstrate giving said substrate surface is an elastomeric thermoplasticurethane; and said top coat is formed from a solvent solution of aplastic selected from the group consisting of acrylics and urethanes. 4.The process of claim 2 wherein said islands have an average diameter ofless than 3000 °A, and said film has at all times a resistance greaterthan 100 megaohms.
 5. An automobile trim component comprising:a. aflexible elastomeric base having a prepared surface; b. minute discreterounded islands comprising indium adhered to said surface, said islandsappearing visually as a continuous film but being electrically isolatedone from another with said film being electrically non-conductive overthe surface thereof, while having a light transmission of less than 25%substantially all of said islands having an average diameter of lessthan 3000 °A and a nominal film thickness of less than 1000 °A; and c. adielectric clear synthetic plastic top coat adhered to said surface andencapsulating and insulating said islands.
 6. The trim component ofclaim 5 wherein said prepared surface is a mirror-smooth light blockingpigmented basecoat and wherein said continuous film is sheeny and lookslike electrodeposited chrome after topcoating.
 7. The trim component ofclaim 5 wherein said flexible elastomeric base is a urethane and saidprepared surface comprises a light-blocking pigmented smooth resinousfilm.
 8. A metallized article comprising:a. a substrate having anorganic surface; b. spaced apart electrically discrete minute islandsthereon of rounded appearance both in plan and elevation view of a metalhaving a melting point in the range of 125° to 250 C. and selected fromthe group consisting of indium and alloys thereof consistingpredominantly of indium, said islands having an average diameter of lessthan 3500 °A and the spatial density thereof being sufficient to impartthe visual appearance of a specular, continuous metal film, the nominalthickness of said metal film being in the range of 150 to 1,000 °A, saidfilm being electrically non-conductive across the plane thereof andhaving a light transmission of less than 25%; c. an intimately adhereddielectric, protective resinous topcoat of a synthetic plastic over saidmetal film encapsulating and insulating said islands one from anotherand affixing them to said organic surface.
 9. The metallized article ofclaim 8 wherein said topcoat has a thickness of at least 1/2 mil. (drybasis) and the electric isolation of said islands prevents transfer ofcorrosion from one island to another upon localized rupture of saidtopcoat.
 10. A vacuum deposited metal layer on a dielectric substratecomprised of:(a) electrically discrete islands of a metal selected fromthe group consisting of indium and alloys thereof consistingpredominantly of indium with substantial non-conductive open regionscompletely surrounding each island, said islands and said open regionshaving a size less than the wave lengths of visible light, said metallayer macroscopically appearing as a continuous metallic film andtransmitting therethrough less than 25% of visible light incidentthereon, and (b) a clear, dielectric resinous protective topcoatthereover (i) having a thickness of at least 1/2 mil (dry basis), (ii)completely filling said open regions, preventing the intrusion thereinof ambient impurities capable of producing an electrochemical corrosionpath thereacross, and (iii) being intimately and firmly adhered to saidsubstrate in said open regions and to said islands.
 11. The metal layerof claim 10 wherein said islands have the appearance of having coalescedin molten phase from smaller nuclei.
 12. A flexible bright automobiletrim component having a non-corroding specular, metal surface of metalselected from the group consisting of indium and alloys thereofconsisting predominantly of indium on an extensible plastic substratecomprising:(a) a mirror-smooth dielectric extensible plastic substrate;(b) a layer thereon of electrically discrete islands of said metal withsubstantial non-conductive open regions completely surrounding eachisland, said islands and said open regions having a size less than thewave lengths of visible light and said layer macroscopically appearingas a continuous metallic film and transmitting therethrough less than25% of visible light incident thereon, and (c) a clear, dielectricresinous protective topcoat thereover (i) having a thickness of at least1/2 mil (dry basis), (ii) completely filling said open regions,preventing the intrusion therein of ambient impurities capable ofproducing an electrochemical corrosion path thereacross, and (iii) beingintimately and firmly adhered to said substrate in said open regions andto said islands.
 13. A vacuum metallized article having a stronglyadhered non-corroding lustrous metal surface of indium, comprising:(a) asmooth dielectric substrate; (b) thin film islands thereon of a metalselected from the group consisting of indium and alloys thereofconsisting predominantly of indium, smaller in diameter than the wavelengths of visible light and having a rounded apperance characteristicof having condensed in liquid phase from small nuclei, each such islandbeing surrounded by an electrically non-conductive open region which issubstantial relative to the size of the island but which is smaller inany dimension than the wave lengths of visible light, said thin filmislands together defining a bright planar surface that (i) iselectrically non-conductive along the plane thereof, (ii) transmits lessthan 25% the visible light incident thereon, and (iii) as deposited isexceptionally corrosion-prone when directly exposed to a moistenvironment, and (c) a light-passing dielectric resinous topcoatthereover intimately adhered to both said thin film islands and to saiddielectric substrate and filling said open region around each island,electrochemically isolating one island from the next.
 14. A vacuummetallizing process producing a non-corroding specular surface of metalselected from the group consisting of indium and alloys thereofconsisting predominantly of indium, comprising:(a) preparing amirror-smooth dielectric substrate; (b) vacuum depositing said metal onsaid substrate to form thereby thin film islands of said metal on saidsubstrate that have a size less than the wave lengths of visible lightbut macroscopicaly appear as a continuous metallic film and transmitless than 25% of visible light incident thereon, said islands coalescingin liquid phase from smaller nuclei and having a rounded appearancecharacteristic of said coalescence; (c) arresting the vacuum depositingshort of the stage whereat said islands coalesce to an electricallyconductive film and while each island is still surrounded by anelectrically non-conductive open region which is substantial relative tothe size of the island but is smaller in any dimension than the wavelengths of visible light; (d) applying a clear dielectric resinoustopcoat in liquid phase ovr said thin film islands and filling said openregion about each island; and (e) setting said topcoat to a continuousprotective film over and between said thin film islands,electrochemically insulating one from another, said topcoat being welladhered to said thin film islands and to said substrate in the areas ofsaid open region about each island.
 15. The process of claim 14 whereinsaid thin film islands have a diameter less than 3000 °A, a nominalthickness in the range of 150 to 1000 °A; and at all times an electricalresistance along the planes thereof of greater than 100 megaohms andwherein said topcoat is at least 1/2 mil thick (dry basis).
 16. Theprocess of claim 15 wherein said dielectric substrate is a basecoatedmolded elastomeric plastic and said topcoat is formed from a solventsolution of a resin selected from the group consisting of acrylics andurethane.